There is a need for compactly structured beam addressable information storage disk drive systems capable of fitting within the half height format of a personal computer drive bay. The problem of achieving this objective is aggravated somewhat by the fact that beam addressable storage disks are rigid plastic disks many times the thickness of flexible ("floppy") disks commonly used as removable storage media for personal computers. Moreover, such disks are generally encased in protective hard shelled cartridges that add to the bulk of the disk assembly that must be accommodated in the drive system.
It is well known to provide disk drive load mechanisms for removable disks that guide the inserted disk downward into engagement with the drive spindle used to rotate the disk during write/read operation. A drawback of this approach is that a relatively large volume of space, both vertically and laterally, must be reserved for the vertical up and down movement of the disk cartridge. This is a particular problem with a beam addressable system since it would require that the height of the optical head be reduced to accommodate the downward moving cartridge. Additionally, peripheral space occupied by the vertically moving cartridge could be used more efficiently to accommodate other components of the drive system.
As a consequence, it is preferable to provide a load mechanism that accepts insertion of the disk in a single plane and moves the drive spindle axially of the disk to drivingly engage the disk hub, without any axial motion of the disk.
U.S. Pat. No. 4,177,491 illustrates one form of a mechanism in which a combined centering cone and drive chuck are moved axially to engage the center of a computer disk. In this mechanism, the cone/chuck mechanism is moved into position on the disk hub along a lead screw formed on the outer surface of a drive spindle stationary by a friction device. The holding force of the friction device is overcome when the chuck engages the disk so that the spindle screw and chuck rotate together to drive the disk. The driving force is provided by an external motor drive engaging the outer circumference of the spindle housing. In the disclosure of this patent, the disk is vertically oriented and the axial movement is horizontal, although the mechanism could just as easily be rotated 90.degree. resulting in vertical translation of the drive chuck.
U.S. Pat. No. 4,482,993 is another example of a mechanism used to move the drive spindle to the disk hub except that, in this case, the drive spindle is raised vertically to engage a horizontal disk. In this disclosure, the spindle and spindle drive motor, assembled together inside a cylindrical enclosure, are translated axially within the cylinder to the disk by an external rotating cam member acting on a follower pin attached to the spindle drive motor housing.
These mechanisms, although accomplishing the objective of engaging the drive spindle to the disk without moving the disk out of its insertion plane, have the problem that they are bulky in design and occupy more space than would be desirable for use in a half height disk drive configuration. Moreover, since they are designed for use with magnetic disks, the operative positioning of the spindle is not of critical concern and no particular provision for this is made in the disclosed mechanisms. In fact, the camming arrangement for the magnetic disk drive of U.S. Pat. No. 4,482,993 would inherently be unable to provide the precise vertical positioning of the spindle which is important in a magneto-optical disk drive. Also, the mechanism of U.S. Pat. No. 4,177,491, with its reliance on frictional clutching/declutching surfaces, may not be suited for practical application where power consumption, wear and heat are critical concerns.
It is important that the disk-engaging surface of an axially translatable drive spindle be precisely positioned during read/write operation along the "z" axis dimension, without any tilt or skewing, since this is critical to the proper focusing of the optical read/write beam on the data surface of the disk. Magnetic disk drives employ read/write heads that are either directly in contact the disk recording surface or ride on air and thus are not subject to this critical requirement.
It is therefore an object of the present invention to provide a load mechanism for a beam addressable information storage disk drive system which overcomes the disadvantages of known disk drive systems of the type described above.
It is another object of the invention to provide a load mechanism for a system of the type described which is compact in design and suitable for use in half height computer drive bay configurations.
It is yet another object of the invention to provide a load mechanism for a system of the type described that orients the disk relative to the read/write optical beam with a high degree of precision so as to minimize the amount of beam focus error correction attributable to disk positioning.